Like the towers you go up against, your units start off simple enough. You begin the game with two units: the first is suited to take heavy fire while dishing out little damage itself, and the second is the opposite, dealing high damage at long range but it's very weak against enemy attacks. After that you'll unlock tanks that are a mix of the first two units, units that generate shields for it and the two units surrounding it. All your units can be purchased as soon as you have enough resources—which you receive after a tower is destroyed or by collecting the resources scattered throughout the battlefield—or you can use your resources to upgrade your current units, increasing their health and firepower.

The maps are divided up by roads that you'll be using to traverse the battlefield. At any time you can press Y and check out a blue overlay of the entire map, complete with enemy tower locations, item drops, and the path you currently have selected. You can alter this path to go in any direction you like. If there's a road, you can guide your convoy down it. This is one of the most important features of the game, and it's where most of the strategy comes into play. It's up to you to choose the best path to your destination. If a road is surrounded by powerful enemy towers, it's probably not the best idea to send your troops down it. There's also the occasional time limit that forces you to quickly go from point A to point B before a bridge it taken out, so in instances like that you'll have to choose the safest path that gets you the most resources.

The iOS and Android versions of Warzone Earth had a single campaign that took you through one of the mysterious anomalies that arrived on earth at the same time the aliens did. In the XBLA, PC, and Mac versions, they've added a handful of levels set in Tokyo, doubling the size of the campaign. The Tokyo levels also add a little extra variety to the levels you'll fight in. On top of that are six exclusive Tactical Trial levels that are essentially virtual training missions. These missions have set rules, units, and abilities you can use, testing your skills and ability to adapt to unique situations.

Anomaly: Warzone Earth was a welcome breath of fresh air for the popular tower defense genre when it released last year, and none of the clever mechanics, gorgeous visuals, and addictive fun were lost during its move to XBLA. This is a must-have for any tower defense fan looking to expand their library, and it's a great first game for any potential newcomers interested in getting in on this incredibly addicting subgenre.